I. Field of the Invention
The invention pertains to the field of fluoropolymer hoses and tubes such as fluoropolymer composite pipes used in fuel lines.
II. Description of the Prior Art
With the advent of increased concern over evaporative fuel emission standards, there has been an increasing need for fuel lines that meet more stringent evaporative emission requirements, while at the same time having high chemical and electrostatic discharge resistance. Further, in order to be economical, any fuel line must be able to be produced in large quantities at a low cost. A desirable fuel line should have appropriate physical properties including, but not limited to, sufficient tensile strength and kink resistance, or the ability of the fuel line to retain a particular shape upon bending.
Fuel line hoses of a variety of materials have been suggested over the years. Tetrafluoroethylene has been utilized and has excellent and outstanding high temperature and chemical resistance. xe2x80x9cHose Technology,xe2x80x9d publisher: Applied Science Publisher, Ltd., Essex England, by: Colin W. Evans, pages 195-211. Nylon has also been utilized as a hose composition. However, fluorinated polymers are difficult to use because of the difficulty in adhering other materials to them in order to form desirable composites.
U.S. Pat. No. 4,933,060 discloses surface modification of fluoropolymers by reactive gas plasma. The reference, however, further indicates that in order to have sufficient bonding, adhesives must be utilized prior to the application of an additional layer. Suitable adhesives are epoxies, acrylates, urethanes, and the like.
U.S. Pat. No. 4,898,638 teaches a method of manufacturing flexible gaskets which withstand chemical agents. Flexible gaskets are prepared in which one film of PTFE (polytetrafluoroethylene) is directly applied onto a sheet of raw rubber and the sheet of rubber together with the film of PTFE is subjected to heating and pressure suitable for causing the rubber to vulcanize. Use of adhesives in the bonding of fluoropolymers is likewise described in U.S. Pat. No. 4,743,327, and their use is required to make the development operative. Activating fluoropolymers utilizing ammonia gas is taught in U.S. Pat. No. 4,731,156.
None of the prior art describes a fluoropolymer with an outer layer of a different polymer that is integral with and chemically bonded to the fluoropolymer, which when combined in a multi-layered composite hose or pipe, has desirable electrostatic discharge resistance, hydrocarbon evaporative emission resistance, and flexibility. Further, the prior art suggests the need for adhesives to firmly and fixedly join plastic layers. This invention does not require additional adhesives to join the fluoropolymer layer to the other polymer layer because the layers are chemically bonded to each other.
Polymer surfaces typically lack the irregular structure necessary to achieve an effective mechanical bond. Therefore, methods such as etching or scuffing have been used to physically xe2x80x9croughenxe2x80x9d the substrate surface. This invention however, by incorporating a chemical bond, does not require this mechanical alteration of the surface. It can be shown through various microscopic techniques (i.e. SEM) that no significant changes occur to the physical structure of the fluoropolymer substrate surface by the various means of surface activation employed in this invention such as exposure to a charged gaseous atmosphere, sodium naphthalate bath, a laser, silane and non-silane coupling agents, and the like. Furthermore, bonding has been achieved by these methods with materials such as thermoset elastomers which typically do not have processing viscosities sufficiently low to achieve adequate bond strength strictly by mechanical means.
It is an object of the present invention to have a fuel pipe or tube that has a fluoropolymer substrate that can be activated sufficiently to be able to have an integral and chemically bonded top coat or layer of a different polymer.
It is also an object of the present invention to prepare a fluoropolymer composite by extruding a multi-layered fluoropolymer substrate, one layer of which has desirable chemical, permeation, and electrostatic discharge resistance, and on top of the fluoropolymer layers would be extruded the different polymer layer.
The present invention is concerned with a method of preparing a fluoropolymer composite tube comprising the steps of:
(1) forming a fluoropolymer substrate;
(2) activating a surface of the fluoropolymer substrate,
(3) and thereafter applying a layer of a different polymer to the activated fluoropolymer such that there exist chemical bonds between the layers.
The fluoropolymer substrate can be activated in a number of ways such as subjecting the substrate to a charged gaseous atmosphere formed by electrically ionizing a gas which contacts the substrate, bathing the substrate in a sodium naphthalate bath, exposing the substrate to silane or non-silane coupling agents, exposing the substrate to a high-energy laser, or combinations thereof. Other means of activation which are known in the art may also be utilized, surface activation being broadly defined to mean those methods which have the effect of altering the electronic states of the surface of the fluoropolymer substrate without mechanically altering the surface. Mechanical alteration would include etching or scuffing the surface. Also, the different polymer can optionally contain a curing agent. Both the activation of the fluoropolymer layer and the addition of a curing agent to the different polymer layer serve to increase the strength of the chemical bonds between the layers.
The invention is also directed to a fuel pipe comprised of an inner fluorocarbon layer having electrostatic discharge resistance and hydrocarbon evaporative emission resistance, and on top of and integral with the fluorocarbon layer is an outer layer of a different polymer layer chemically bonded to the fluorocarbon layer.